The present invention relates to aromatic polyester compositions having a reduced tendency to drip upon burning. More particularly, the present invention relates to the incorporation of a polyhydroorganosiloxane into a polyalkylene terephthalate to provide for the production of a thermoplastic aromatic polyester molding composition exhibiting reduced tendency to drip upon burning.
Prior to the present invention, linear aromatic polyesters, such as poly(1,4-butylene terephthalate) resins, have been recognized as valuable injection moldable thermoplastics. Although these aromatic polyesters have been found to be useful in many applications, these polymers have a tendency to readily burn when ignited. In addition, aromatic polyesters have a tendency to drip when burning which can create flaming droplets of polymer and rapidly propagate fires. Abolins, U.S. Pat. No. 3,671,487, shows that the combination of glass re-enforcement, a flame retardant additive and polytetrachloroethylene resin can be used to overcome the flammable nature of linear polyester resin.
It was further found by Dolce, U.S. Pat. No. 4,344,878, that the flammability and dripping tendencies of burning linear polyesters, such as high molecular weight polymers of terephthalic acid and isophthalic acid could be retarded if a minor amount of polytetrafluoroethylene resin were employed in combination with a flame retardant additive.
Although improvements in the flame retardance and non-drip properties of aromatic polyesters have been achieved by the prior art, it has been found that the presence of halogenated flame retardants and non-drip additives in aromatic polyester often can result in production of deleterious by-products when the aromatic polyester is burned. Considerable effort therefore has been made by the thermoplastic industry to develop non-halogenated additives for aromatic polyesters to improve the ability of such polymers to resist rapid propagation of fire upon burning.